House electric



March 19, 1929. HARVEY 1,705,728

MOTOR CONTROL SYSTEM Filed Feb. 20. 1923 bu /3 w /0 WITNESSES: INVENTOR 1406/2 L Harv: y.

W v BY %Z/ J m/ ATTORNEY Patented Mar. 19, 1929.

UNITED STATES PATENT OFFICE.

ALBERT L. HARVEY, OF WILKINSBURG, PENNSYLVANIA, ASSIGNOR TO WESTING- HOUSE ELEGTRIG 8: MANUFACTURING COMI'ANY, A CORPORATION OF PENNSYL- VANIA.

MOTOR-CONTROL SYSTEM.

Application filed February 20, 1923. Serial No. 620,129.

My invention relates to motor-control syswith operating coils 12 and 13. The enertems and it has particular relation to control gizing circuit of coil 13 is normally intersystems subject to considerable variation in rupted by a condenser 10, the purpose of line voltage. which will be hereinafter described.

The object of my invention is to afford suit- In order that the advantages of my invenable protection to motors subjected to sudtion and the necessity for such protection may den increase in current, particularly in the be morereadily understood, it may be assumed armature circuit, by reason of fluctuations in that 550 volts is the normal line voltage. It lt may also be assumed that, by reason of vary- I" In such applications as mine gathering ing load conditions in a railway circuit, the

pumps, the voltage condition are often very voltage fluctuates between a maximum of 600 bad on account of the factthat power is volts andaminimum of 450 volts. If, at one usually obtained from railway circuits. As instant, the motor is operating in accordance a result of suchfluctuations in voltage, curwith a line potential of 450 volts and is de- 15 rent variations are produced in accordance veloping a counter-electromotive force of say 100 volts, the effective voltage impressed on E the armature is 50 volts and, if the resistance R is equal to 1 ohm a current of 50 amp, ac- R cording to the above-mentioned formula,

with Ohms law,

20 in which E is equal to line voltage minus the B e armature 1.

counter-electromotive force of the motor con- NOW 8111313058 at the IleXt n n h a lnected thereto and R is the resistance of the y l 18 udden y lifted andthe line voltond to l di to th motor l th i age rises to 600 volts. Before 1t is possible for t 1 resistance f th motor armature, the motor to accelerate and develop additional 25 At th nt ti la number f counter-electromotive force, there is an inpumping tfit are d i b l lt t ti stantaneous voltage impressed on the armaa0 direct-current 1n0t01- That is to ay, no 131116 equal to 600 VOltS 111111118 the VOltS controller or automatic starter is employed. m lve force- B being a con- In order, therefore, to Protect, the notor, stant the momentary armature 01111281. is 200 when running normally, against fluctuation amp which 1s the result of lmpressmg an efin current caused by changes in impressed fGCtHG voltage upon the armature equal to 5 voltage, it is common practice to permanentf r tlmes the normal eifective impressed 1y onn t i t h as water 1 voltage. It is well understood that such a stat, in the armature circuit. fluctuation in current is very undesirable and To avoid th u of a p r a t t l it is the purpose of my 1nvent1on to limit the resistor I propose to employ automatic eleccurrent to a safe value.

' trorespons1ve means for inserting a resistor I accordance with my invention, I employ in the armature circuit during periods of abr y 1 that is atively small and may be o m l v ltag d to remove id i t designed to respond readily to fluctuations in from circuit upon the restoration of normal Voltage nd urrent. The operating or curvoltag ondition rent coil 12 is preferably connected in the My invention will be best understood by circuit Qf armature 1, and a voltage C011 13 .15 reference to the accompanying drawing in connected in circuit with condenser 10. Coils which the single figure is a diagrammati 12 and 13 are commonly termed series and view of, circuits and apparatus embodying sh nt, respectively.

m invention. When normal voltage obtains in line con- 10o ith reference to the drawing, a motor havductors 4 and 5, switch 7 is closed, its operating an armature 1, a shunt field-magnet windmg coil 8 being fed through relay 11 from coning 2 is operatively connected to line conducductors 4 and 5. Upon the occurrence of abtors i and 5 through an auxiliary resistor 6, normal voltage sufiicient to charge condenser An electromagnetic switch 7 is arranged for 10, coil 13 will be energized to such an extent controlling resistor 6 and is provided with that it will assist series coil 12 to actuate rela an operating coil 8. A11 auxiliary relay 11 is 11, thereby interrupting the circuit throng adapted to control switch 7 and is provided coil 8 and efiecting the opening of switch 7 for the urpose of inserting resistor 6 in circuit wit armature 1 thereby limitin the motor current as will he readily appreciated.

hen normal voltage is restored, condenser 10 discharges its energy to deenergize coil 13 and, as soon as normal current flows in the circuit of armature 1, the excitation of coil 12 is sufliciently reduced to release and restore relay 11 to its illustrated position, whereupon switch 7 is reclosed.

According to my system, the use of a permanently connected resistor becomes unnecessary, and the efiect of a condenseras herein employed serves to insure a positive and quick operation of the protective apparatus, automatically, in accordance with the value of voltage impressed upon themotor. I c

aim as my invention: .1. In a protective system the combination with a motor having an armature, of a resistor connected in circuit therewith, a switch for controlling said resistor, el'ectroresponsive means for controlling sa d switch, and means comprising a coil and a condenser 1n c1rcu1t therewith for rendering the electroresponsive means effective upon sudden variations in voltage.

2. In a protective system the combination with a motor having an armature, of a resistor therefor, a switch for controlling said resistor, a series coil for controlling said switch, a second coil for assisting the series coil, and a condenser for controlling said second coil in accordance with sudden variations in voltage impressed upon said motor.

3 The combination with a motor having an armature, of a protective resistor therefor, a switch for controlling said resistor, a relay for controlling said switch having an operating coil responsive to the motor armature current, a coil for assisting said relay coil, and a condenser for controlling the last named coil in accordance with sudden variations in voltage impressed upon said motor.

In testimony whereof, I have hereunto subscribed my name this 14th day of February,

ALBERT L. HARVEY. 

